import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

class Message {
    public String from;
    public String to;
    public String message;
}
@WebServlet("/message")
public class MessageServlet extends HttpServlet {
    private ObjectMapper objectMapper=new ObjectMapper();
//     改成数据库，就不需要这个变量了
    //private List<Message> messages=new ArrayList<>();
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理提交消息的请求
       Message message= objectMapper.readValue(req.getInputStream(),Message.class);
      //最简单的保存方法是保存到内存中
//       messages.add(message);
       //通过ContentType告知页面，返回的数据是json格式
        save(message);
       resp.setContentType("application/json;charset=utf8");
       resp.getWriter().write("{\"ok\":true}");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取到消息列表，只要把消息列表内容整个给返回客户端即可
        //此处需要使用objectMapper把Java对象，转成json格式字符串
        List<Message> messages=load();
        String jsonString=objectMapper.writeValueAsString(messages);
        System.out.println("jsonString: " + jsonString);
        resp.setContentType("application/json;charset=utf8");
        resp.getWriter().write(jsonString);
    }

    private void save(Message message){
        //把一条消息保存在数据库中
        Connection connection=null;
        PreparedStatement statement=null;
        try {
            //1.与数据库建立连接
             connection=DBUtil.getConnection();
            //2.构造SQL
            String sql="insert into message values(?,?,?)";
             statement=connection.prepareStatement(sql);
            statement.setString(1,message.from);
            statement.setString(2,message.to);
            statement.setString(3,message.message);
            //3.执行sql
            statement.executeUpdate();
            //4.释放资源

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,null);
        }
    }

    private List<Message> load(){
        List<Message> messages=new ArrayList<>();
        //从数据库中获取到所有的消息
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;
        try {
            connection=DBUtil.getConnection();
            String sql="select * from message";
            statement=connection.prepareStatement(sql);
            resultSet=statement.executeQuery();
            while(resultSet.next()){
                Message message=new Message();
                message.from=resultSet.getString("from");
                message.to=resultSet.getString("to");
                message.message=resultSet.getString("message");
                messages.add(message);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return  messages;
    }


}
